I'm pretty sure it just knocks some out, in order to start new promotions... Don't think it has anything to do with how many sponsors are in the game, or being a financial/roster issue.
Each promotion can have a max of 4 sponsors... With the game only allowing 35 promotions, the max amount of sponsors needed should be 140... But, most of the updates I do have 34 in them, so you only really need 136... I'm pretty sure there are 263 sponsors in the game... So about double the amount.
-Bill
Thanks for clearing that up Bill. I guess its just the nature of the game to recycle promotions... Oh well, it was an exciting prospect for me for a few hours